On Fri, Aug 9, 2024 at 10:01 PM Jaroslav Kysela perex@perex.cz wrote:
On 09. 08. 24 14:52, Pierre-Louis Bossart wrote:
And metadata ioctl can be called many times which can meet the ratio modifier requirement (ratio may be drift on the fly)
Interesting, that's yet another way of handling the drift with userspace modifying the ratio dynamically. That's different to what I've seen before.
Note that the "timing" is managed by the user space with this scheme.
And compress API uses codec as the unit for capability query and parameter setting, So I think need to define "SND_AUDIOCODEC_SRC' and 'struct snd_dec_src', for the 'snd_dec_src' just defined output format and output rate, channels definition just reuse the snd_codec.ch_in.
The capability query is an interesting point as well, it's not clear how to expose to userspace what this specific implementation can do, while at the same time *requiring* userpace to update the ratio dynamically. For something like this to work, userspace needs to have pre-existing information on how the SRC works.
Yes, it's about abstraction. The user space wants to push data, read data back converted to the target rate and eventually modify the drift using a control managing clocks using own way. We can eventually assume, that if this control does not exist, the drift cannot be controlled. Also, nice thing is that the control has min and max values (range), so driver can specify the drift range, too.
And again, look to "PCM Rate Shift 100000" control implementation in sound/drivers/aloop.c. It would be nice to have the base offset for the shift/drift/pitch value standardized.
Thanks.
But the ASRC driver I implemented is different, I just register one sound card, one device/subdevice. but the ASRC hardware support 4 instances together, so user can open the card device 4 times to create 4 instances then the controls can only bind with compress streams.
I think I can remove the 'SNDRV_COMPRESS_SRC_RATIO_MOD', Only define a private type for driver, which means only the ASRC driver and its user application know the type.
For the change in 'include/uapi/sound/compress_params.h", should I keep them, is there any other suggestion for them?
Best regards Shengjiu Wang
Jaroslav-- Jaroslav Kysela perex@perex.cz Linux Sound Maintainer; ALSA Project; Red Hat, Inc.